The present invention relates to an electrical cable with a temperature sensing means, and more specifically, to an electric cable that utilizes an optic fiber temperature sensing means placed longitudinally in the cable and having at least one strength member to provide additional protection for the optic fiber. It is desirable to accurately measure the temperature of a cable because the amount of electrical current that can be carried by a cable is limited by temperature. With accurate information regarding cable temperature, utility companies can make better use of their infrastructure.
It is relatively easy to estimate the temperature of a known conductor cable in a steady state ambient air temperature. In contrast, it is extremely difficult to determine the temperature of a cable under real world operating conditions due to the influence of wind, rain, solar radiation, and ever changing ambient air temperatures.
Conventional methods for measuring cable/conductor temperatures include Valley Group CAT-1 Tension Monitor, the EPRI Video Sagometer, and the USI donut. The CAT-1 method measures cable tension and weather conditions and the calculates the expected cable temperature using a thermal model. The EPRI Video Sagometer measures the cable sag and then calculates the expected cable temperature using a thermal elongation model. The USI donut uses two thermocouples placed on the outside surface of the transmission cable to measure its temperature at a single point. None of these methods measure the internal temperature of the cable/conductor or give real time temperature data for the length of the cable. Furthermore, they fail to satisfactorily measure cable temperature axially and radially throughout the entire length of the cable as can be obtained by the present invention.
The following U.S. patents describe temperature sensing with fiber optics and/or detail cables having optic fibers and electrical conductors.
U.S. Pat. No. 5,696,863 details fiber optic methods and devices for sensing physical parameters, like temperature or force.
U.S. Pat. No. 5,991,479 details distributed fiber optic sensors to measure temperature at different points along the fiber.
U.S. Pat. No. 4,852,965 details a composite optical fiber-copper conductor, which includes one or more reinforced optical fiber units and one or more metallic conductor pairs enclosed in a sheath system.
U.S. Pat. No. 4,952,020 details a ribbon cable having optical fibers and electrical conductors spaced side to side within a flexible jacket.
U.S. Pat. No. 5,029,974 details a gel-filled plastic buffer tube for carrying optical fibers.
U.S. Pat. No. 5,651,081 details a composite fiber optic and electrical cable having a core which loosely contains at least one optical fiber, one or more electrical conductors having an outer polymer insulating layer, one or more strength members, and a surrounding protective jacket.
U.S. Pat. Nos. 5,917,977 and 6,049,647 detail a composite cable having a conductor and at least one fiber optic conductor in the core.
U.S. Pat. No. 6,072,928 relates to a tow cable for measuring temperature in a water column having a fiber optic core, an electrically conducting polymer jacket, and a temperature sensor embedded in the polymer jacket.
U.S. Pat. No. 6,236,789 details a composite cable for access networks having one or more buffer tubes, each buffer tube encircling at least two optical fibers for supplying optical signals to at least two of the units, each unit having electrical current and voltage requirements. The cable has a layer of S-Z stranded electrically insulated conductors around the buffer tube or tubes. The number of pairs of conductors is less than the number of active optical fibers which excludes conductor spares. Preferably, the buffer tubes are S-Z stranded. The cable also includes a strength member and an outer plastic jacket encircling the buffer tubes, the conductors and the strength member.